I originally was using the "hsMmcSdRw" project to try to interface with the uSD card, but switched to the "boot" project provided by starterware and now I can use read and write to the uSD card using the FATfs commands.
The hsMmcSdRw project uses linux commands through the UART to interface with the uSD card, but still calls the same functions, so I'm not sure if it's a card version issue unless the way they initialize the cards are different. We did purchase some lower capacity uSD cards and plan to try them in the near future.